I agree with you totally that it would be almost beyond belief for Kirk not to notice Spock's absence during that scene.
All I'm saying is the way it's filmed, from the close up of Spock's face at he quickly weighs his options and acts on his own, to the fact he sort of breezed behind Kirk into the turbolift when Kirk was distracted by telling Sulu to get us the hell out of here, and most glaringly the fact he seemed to only realize Spock was gone when McCoy called and he noticed the empty chair all seem to strongly indicate the film makers intent was to imply Kirk didn't even notice Spock was gone.
Like I said it's almost beyond belief to think Kirk wouldn't notice, but that's the way the shooting of the film looks like it wants us to think
Like I said either way it's a great scene and it's not a deal breaker, just a little nagging detail I've never really been able to decide one way or the other for sure.
As long as you stop saying it was 6 minutes when the script says it was 3 and a half.
You got it
I also won't refer to the point when Kirk (sitting in his chair with his arms folded like "Well can't do shit now, so I'm just going to sit here and wait for the end") asks Savvik for a time mark and she replies 3 minutes 30 seconds and since David said it was a four minute countdown we can safely assume there are only 30 seconds left, assuming Savvik was right on the mark time wise. And in that 30 seconds.
1. Kirk asks Chekov the distance from Reliant to which Chekov replies 4,000 kilometers.
2. Sulu says "We're not going to make it are we" and Kirk is able to look over at David who shakes his to confirm they're dead.
3. Khan is able to go on his last rant about how they cant get away and stabbing and spitting at thee and have the camera linger on him for 2 or 3 seconds after his last word.
4. Spock is able to complete his repairs and replace the lid to the mains.
5. A junior officer informs Kirk that the mains are back on line
6. Kirk says "bless you scotty, go sulu" and sulu is able to engage the warp engines and still have 3 or so seconds before Reliant explodes.
I'm sure if I time it it'd be 30 seconds right on the nose just like the script says